农业污水灌溉对石家庄市近郊灌区地下水环境的影响

Effects of Wastewater Irrigation on Groundwater Quantity and Quality in the Suburbs of Shijiazhuang City,China

如何在水资源匮乏的干旱,半干旱地区合理有效地利用城市污水不仅是一个资源再生的问题,同时也是一个保护环境,使区域经济保持可持续发展的问题。本文作者通过对石家庄市近郊具有几十年污水灌溉历史的典型灌区的地下水进行了采样分析,评价了华北平原区农业污水灌溉对区域地下水环境的影响。首先,简要回顾了各国污水利用的历史和现状,比较了有关使用城市污水灌溉的利弊。然后,在对比确认污水灌溉对地下水的补给效果的基础上,基于电导率、硝酸根以及溶解氧浓度的测试结果,分析了污灌区地下水的水质变化特性。在污水灌溉区的硝态氮浓度很高,分布在35mg/l^130mg/l范围内,井深小于40m的井水的硝酸根离子浓度超标率为100%。而在用地下水进行灌溉的地区,硝酸根离子浓度都在35 mg/l以下。此外,经过长期污灌的地区,地下水水化学类型已从原有的重碳酸硫酸钙(钙镁)型水演变成了重碳酸氯化钙(钙镁)型水,矿化度也比较高。在一般情况下,由于城市污水来源是连续的,而农作物需水是有季节性的。在作物非生长期,污水很容易进入地下水。这可能是造成长期利用污水灌溉的地区水化学性质改变的主要原因。

The rational use of swage waters from urban areas in arid and semi-arid regions that are in short of water is not only the key for comprehensive use of water resources, but also the key for regional environmental protection and sustainable development. In order to assess the impacts of wastewater on regional groundwater system, swage water, groundwater samples were taken and analyzed in typical croplands in the North China Plain where urban wastewater or groundwater have been used for irrigation for several decades. Firstly, the use of wastewater for agriculture has both interesting economical benefits and constraints. Once the wastewater are directed to agricultural fields, the pressure on high-quality water resources decreases, contributing to solutions ofrelated to water availability problems, especially in those areas where clean water is difficult to obtain. However, the general constraints in irrigation with wastewater focus on human and environmental health hazards. Secondly, groundwater flow system in the study area was analyzed by considering the state of the art and current perspectives for croplands irrigation. For example, the water table in the groundwater irrigation area decreased continuously at a rate of 0.7m/year from 1992 to 1999. However, the water table in the wastewater irrigation area changed much less at the same period. It means that the wastewater irrigation practices have a great contribution tofor recharging the local groundwater. BThen, based on the analyzedthe results of EC, DO and nitrate concentrations in the groundwater, it was found that nitrate concentrations in groundwater ranged from 50 to 130 mg/L in wastewater irrigation area, and less than 35 mg/L in groundwater irrigation area, respectively. Especially, nitrate from all the wells that were shallower than 40 m in wastewater irrigation area exceeded the drinking water standard set by WHO. The regional temporal and spatial trends of the nitrate patterns can be explained by considering land use, irrigation practices and other chemicals. Finally, it also found that hydrochemistry for groundwater has changed from Ca（ ＋ Mg）-HCO3 ＋ SO4 type into Ca（ ＋ Mg）-HCO3 ＋ Cl type with long term wastewater irrigation practice. It can be considered that the constraint hampering a direct link between wastewater production and agricultural use is the gap between wastewater supply and agricultural demands with respect to day- and night flow, but more importantly to seasonal variations. Because wastewater was produced continuously while the demand for irrigation water depended on the season and the crop growth stage, much wastewater infiltrated in to groundwater in off-out of growth season. Therefore, wastewater has great harmful influences onto the regional groundwater quality for the long termlong-term application of wastewater irrigation practices.